Aggression- Neural And Hormonal Influences Flashcards
What are the two neural influences
The limbic system
The hippocampus
What are two key structures in the limbic system that are associated with aggression
The amygdala
The hippocampus
What is the limbic system
an area of the brain that helps to coordinate behaviours that satisfy motivational and emotional urges
What is the amygdala responsible for
quickly evaluating the emotional importance of sensory information and prompting an appropriate response
What happens if certain areas of the amygdala are simulated electrically
an animal responds with aggression such as snarling and adopting an aggressive posture
What happens if certain areas of the amygdala are surgically removed
the animal no longer responds to stimuli that would have previously led to rage
Who looks at if certain areas of the amygdala are surgically removed
Kluver and Bucy 1937 discovered that the destruction of the amygdala in a monkey who was dominant in a social group caused it to lose its domination place in the group
What does Kluver and Bucy 1937 discover
The destruction of the amygdala in a monkey who was dominant in a social group caused it to lose its domination place in the group
What is the hippocampus involved in
Formation of long-term memories and so allows an animal to compare the conditions of a current threat with similar past experiences
What does an impaired hippocampal function prevent
The nervous system from putting things into a relevant and meaningful context and so may cause the amygdala to respond inappropriately to sensory stimuli resulting in aggressive behaviour
What did Boccardi 2010 find
That habitually violent offenders exhibited abnormalities of hippocampal functioning
What does serotonin do in normal levels
exerts a calming inhibitory effect on neuronal firing in the brain, it typically inhibits the firing of the amygdala the part which controls fear, anger and other emotional responses
What does serotonin do in low levels
remove the inhibitory effect with the consequence that individuals are less able to control aggressive behaviour - serotonin deficiency hypothesis
Also associated with an increased susceptibility to impulsive behaviour aggression and even violent suicide
what does the serotonin deficiency hypothesis result in
when the amygdala is simulated by external events it becomes more active causing the person to act on their impulses and making aggression more likely
How does serotonin reduce aggression
By inhibiting responses to emotional stimuli that might otherwise lead to an aggressive response
What does Mann et al 1990 do
Gave 35 healthy participants dexfenfluramine using a questionnaire to assess hostility and aggression levels they found that this in males was associated with an increase in hostility and aggression scores
What is dexfenfluramine known as
deplete serotonin
Name a hormonal influences
Testosterone
What is testosterone
produces male characteristics one of which is aggressive behaviour and is said to peak in young males and then decline
Who looked at testosterone
Sapolsky 1998
Dabbs et al 1987
Carre and Olmstead 2015
What did Sapolsky 1998 do?
How removing the source of testosterone in different species typically resulted in much lower levels of aggression
Subsequently reinstating normal testosterone levels with injections of synthetic testosterone led to a return in aggressive behaviour
What did Dabbs et al 1987 do and find?
Measured salivary testosterone in violent and non-violent criminals
Found that those with higher testosterone had a history of primarily violent crimes whereas those with lower levels only had committed non-violent crimes
What did Carre and Olmstead 2015 do?
claimed that testosterone concentrations are not static but fluctuate rapidly in changes in social environment.
What do all the studies show for testosterone?
Changes in test levels appear to influence aggressive behaviour by increasing amygdala reactivity during the processing of social threat.
What evidence is there for the role of the amygdala in aggression
Pardini et al (2014)
What did Pardini et al (2014) find?
The participants with lower amygdala volumes exhibited higher levels of aggression and violence
So reduced amygdala volume can predict the development of severe and persistent aggression
What did Pardini et al (2014) do?
longitudinal male participants from child to adult
Participants with varying histories of violence were subjected to an MRI at age 26
Who looked at evidence for the role of the hippocampus in aggression?
Raine et al 2004
What did Raine et al do?
studies 2 groups of violent criminal those who faced conviction (unsuccessful) and those who evaded the law
MRI Scans
What did Raine find
asymmetries in the hippocampus in the unsuccessful group the hippocampus in either hemisphere differed in size, an imbalance presumed to have arisen early in brain development
What did researchers suggest the asymmetry found in Raine’s study
might impair the ability of the hippocampus and the amygdala to work together so that emotional information is not processed correctly leading to inappropriate verbal and physical responses as a result
give two ways in which you would evaluate hormonal influences
inconsistence in evidence
aggression or dominance
Explain inconsistency in evidence to evaluate hormonal influences
studies such as Albert et al 1994 + Olweus 1988 found a positive relationship between test + self reported and likelyhood of responding aggressively to provocation aggression however no correlation was found between test levels and actual violent behaviour among inmates in prisons suggesting relationship between test and aggression in humans is unclear
Who looked at aggression or dominance as a way to evaluate hormonal influences
Mazur 1985
What did Mazur 1985 suggest
we should distinguish aggression from dominance and aggression is one form of dominant behaviour lading to support the idea that rather than directly increasing aggression testosterone promotes statue seeking behaviour of which aggression is a type
What is the difference between acting aggressively and acting dominated said by Mazur 1985
someone acts aggressively with the intent to inflict injury whereas someone acts dominantly to maintain status or achieve status
Who gives research support for the serotonin deficiency hypothesis
Duke et al 2013
What did Duke et al 2013 do?
Meta-analysis of 175 studies involving 6500 participants
What did Duke et al 2013 find?
A small inverse relationship between serotonin levels and aggression, anger and hostility
The magnitude of the relationship varied with the methods used to assess serotonin functioning with year of publication and with self-reported versus other-reported aggression.
Only other- reported aggression was positively correlated to serotonin functioning
What does Duke et al 2013 studies suggest?
the relationship between serotonin and aggression is more complex than originally thought
Who looked at support for the serotonin deficiency hypothesis in non-humans ?
Raleigh et al 1991
What did Raleigh et al 1991 find?
Vervet monkeys fed on experimental diets high in tryptophan exhibited decreased levels of aggression
individuals fed on diets that were low in tryptophan exhibited increased aggressive behaviour
What did Raleigh et al 1991 results suggest ?
the difference in aggression could be attributed to their serotonin levels
In Raleigh et al 1991 study what does tryptophan do ?
increases serotonin levels in the brain
